1. Field of the Invention
The present invention is directed to compositions and methods for treating produce to inhibit and eliminate browning reactions. In particular, the present invention is directed to compositions and methods for treating produce with a synergistic composition including cysteine to inhibit enzymatic and non-enzymatic browning reactions during the processing of produce.
2. Discussion of Background and Material Information
As is well known in the food industry, most produce, i.e., fruits and vegetables, such as potatoes, and particularly dehydrated potatoes, have a pronounced tendency to discolor to a grayish-brown upon prolonged periods of storage. This discoloration phenomenon is commonly referred to as a "browning reaction". Although the discolored produce is neither toxic, nor lacking in nutritive value, the discoloration nevertheless gives the produce an objectionable appearance and flavor which makes the produce unacceptable to a majority of prospective consumers. The various causes for browning reactions have been the object of considerable study over the years, and it is generally agreed that there are two primary reactions responsible for such discoloration of produce, i.e., enzymatic action, and certain non-enzymatic processes.
With respect to the former, i.e., enzymatic browning, it is believed that the deleterious changes manifested in stored produce are attributed to various chemical reactions catalyzed by the enzymes naturally present in the plant material. Typically, most fruits and vegetables are subjected to various processing techniques wherein they are subjected to disorganization of their natural structure, as by peeling, cutting, comminuting, pitting, pulping, freezing and dehydrating. As a result, the produce tends to suffer deteriorative changes including the development of dark and unnatural colors, because the disorganization of the natural structure disrupts the natural segregation of substrates and enzymes, and thus permits the enzymes to contact various substrates with the previously-mentioned results.
In general, for these reactions to occur in fruits and vegetables, there must be sufficient enzyme, substrate and oxygen. Certain fruits, such as kiwi fruit and sunbeam peach, do not tend to brown because they have no substrate. Cantaloupe and oranges do not brown because of low enzyme activity at the pH of these fruits. The browning in avocados is believed to be controlled by their phenolase activities.
In potato processing, it has been observed that substantial enzymatic browning occurs if the surfaces of the potatoes are exposed to oxygen prior to cooking. Enzymatic breakdown also occurs in diseased or bruised potato tubers. In potatoes, it is believed that polyphenol oxidase, i.e. phenolase, enzymes catalyze the breakdown of the substrates chlorogenic acid and tyrosine, to quinones and other compounds which can react with amino acids in a similar manner as sugars to produce Maillard reaction products.
Over the years, various techniques have been used for preventing or inhibiting enzyme activity. For example, it is conventional in the food industry to subject raw fruit or vegetables to blanching with steam or hot water so as to inactivate the enzymes. Although this treatment is generally effective, blanching has the disadvantage that the produce is at least partially cooked so that it no longer tastes like fresh food. In addition, the blanching may also cause leaching of valuable nutrient materials from the produce.
The use of sulfiting agents, such as sulphur dioxide and sodium bisulfite, to inactivate enzymes is also well known in the industry. Indeed, sulfite is believed to be the most effective chemical additive used to prevent enzymatic discoloration in most produce, and particularly potatoes and some fruits. In addition to sulfiting agents, other chemical preservation agents have been used for this purpose. Representative examples of such chemical preservation agents include discoloration inhibitors such as ascorbic acid, citric acid, sorbic acid, and malic acid, in addition to other additives such as salt, EDTA, dextrose, calcium chloride, sodium acid pyrophosphate and sodium citrate. However, none of these discoloration inhibitors have been found to be as effective as sulfites.
Use of these reagents, however, has the disadvantage in that the flavor of the food is typically affected to some degree and at times in an adverse, objectionable manner.
Notwithstanding effective treatment to inhibit enzymatic browning in produce, many types of produce, such as potatoes, which contain sugars and amino compounds, still suffer from browning, particularly in the dehydrated state. This is a paramount concern for the produce dehydrator, and particularly the potato processor, because certain types of potatoes tend to brown more than others.
In this regard, one of the most studied chemical changes in food products is the reaction of amino acids and sugars, first observed and described by Louis Camille Maillard, for whom the Maillard reaction is named. The Maillard reaction begins with sugars and amino compounds forming a reactive intermediate, i.e. 1-amino-1-deoxy-2-ketose, which breaks down by several alternative reaction pathways to form brown polymers, i.e., melanoidins. This type of non-enzymatic browning is one of the major causes of off-flavor in produce, and particularly in dehydrated potatoes.
Prior attempts to combat the discoloration of potatoes, and other produce which tend to experience browning reactions, includes pre-treatments with a sulfiting agent, such as sulphur dioxide, sodium bisulfite and/or sodium sulfite. It has also been proposed to protect produce against such browning reactions by treatments with other chemical agents and preservatives including sodium dithionite, sulfur, bromine, potassium bromate, furfuryl mercaptan, 2-mercaptoacedic acid, 3-mercaptopropianic acid, 4-mercaptobuteric acid, 1-propamthiol, ethane thiol, 2-mercaptoethonol, and iso-amyl nitrite. It is believed that these compounds exhibit an effect in preventing the formation of 1-amino-1-dioxy-2-ketose in the Maillard reaction. Sulfur dioxide is believed to accomplish this by attacking the double bonds of fructosamino acid.
Related to this, the prior art is replete with numerous patents which have attempted to overcome the problems of browning of produce. For example, U.S. Pat. No. 2,890,120, MAKOWER, treats edible plant material with an aqueous solution containing alcohol, alkyl benzine sodium sulphinate, and sufficient hydrochloric acid to give the solution a pH of 1.5. U.S. Pat. No. 2,893,878, SIMON, is directed to a process for treating potatoes with calcium chloride and a water-soluble sulfiting agent dissolved in water in such concentration as to deposit certain effective amounts of calcium chloride and sulphite on the potato to protect the potato against non-enzymatic discoloration during storage. U.S. Pat. No. 2,475,838, JOHNSON, treats fruit with a sulfiting agent, ascorbic acid, and an inorganic chloride to prevent browning. U.S. Pat. No. 2,857,282, JANSEN, treats edible plant material with N-acyl derivatives of mercapto amines which exhibit the ability to inhibit enzyme activity and thus prevent deleterious changes, such as browning, normally caused by enzyme action. U.S. Pat. No. 2,860,055, JANSEN, treats edible plant material with an enzyme inhibiting agent containing aliphatic compounds containing 1-mercapto radicals in a particular spatial relation to another mercapto radicals. U.S. Pat. No. 2,874,059, POWERS, treats produce with an aqueous solution containing salt and citric acid in order to inhibit browning. U.S. Pat. No. 3,987,208, RAHMAN, treats lettuce for use in salads with an aqueous solution of sodium meta bisulfites, citric acid, ascorbic acid and potassium sorbate so as to extend the storage life of the cut lettuce. U.S. Pat. No. 2,620,277, SCALERA, is directed to the treatment of peeled white potatoes with a solution of sodium sulphite and citric acid to prevent discoloration. U.S. Pat. No. 3,049,427, FELLERS, contacts vegetables with a solution of a soluble compound of ethylene diamine tetraacetic acid during a blanching operation so as to minimize the discoloration of processed potatoes. U.S. Pat. No. 4,097,612, POWRIE et al., treats potatoes with an aqueous solution of citrate in combination with sulphur dioxide, followed by immersion in an aqueous solution of an alkali metal pyrophosphate, and optionally a reducing saccharide, followed by immersion in an aqueous solution of an alkaline earth metal salt, and optionally an alkali metal chloride, so as to enhance the retention of potato whiteness, in addition to improving other organoleptic characteristics of the tuber.
As previously mentioned, the dehydrated potato industry has a particularly acute concern for preventing browning of the potatoes, which would otherwise render commercial dehydrated potato products unsuitable for extended storage prior to consumption. In this regard, the assignee of the instant application has used sulfur dioxide as a preservative in potato granules to stop non-enzymatic browning since its entry into the potato processing industry. Representative samples of patents which disclose the use of sulfiting agents in dehydrated potato processes include U.S. Pat. No. 3,027,264, IRMITER et al.; U.S. Pat. No. 3,220,857, HOLLIS, Jr. et al.; U.S. Pat. No. 3,343,970, PADER; and U.S. Pat. No. 3,968,260, SHATILA et al., the latter embodying prior attempts of the assignee of this application to produce low-sulfite dehydrated potato granules.
Cysteine has also been used as a food additive in various processed food products. In most applications, cysteine and other amino acids are incorporated for their flavoring effect. In this regard, U.S. Pat. No. 4,218,487, JAEGGI, is directed to synthetic flavorants made by heating a mixture of an amino sugar, cysteine or cysteine hydrochloride, a polyalcohol and/or water. U.S. Pat. No. 3,681,088, KATZ et al., is directed to a flavoring composition containing thiazo-based flavoring agents in combination with cysteine hydrochloride. U.S. Pat. No. 3,214,276, SAKAKIBARA et al., disclose the use of sodium cysteine-S-sulfinate as a food seasoning composition.
In addition to the common usage of cysteine as a flavoring ingredient, cysteine is also recognized for its effect on the color and preservation of the various animal flesh food products. In this regard, U.S. Pat. No. 3,851,078, KHAYAT et al., disclose that cysteine may enhance the color of tuna-type fish. U.S. Pat. No. 3,552,978, INKLAAR, discloses that cysteine, among other monobasic amino acids, are effective in improving color retention in meat-containing food. U.S. Pat. No. 3,637,772, KLAUI et al., disclose that anti-oxidants are often employed in combination with synergists, including cysteine. The BRAVERMAN, Introduction to the Biochemistry of Foods (Elsevier Publishing Co., New York 1963 pp. 246-247) publication discloses that cysteine, as well as certain other amino acids, have been suggested as an alternative to sulphur dioxide and sulfites for preventing oxidation.
L-cysteine HCl has been used in food products over the last 25 years. For example, L-cysteine HCl is approved in bakery products in amounts up to 0.009% of the flour used as a dough conditioner and as a nutrient supplement. L-cysteine HCl has also been used to prevent discoloration in pears, onions, fruit concentrates, as well as other foods. Related to this, L-cysteine, L-cystine and their derrivatives have been used in bakery products to enhance dough softening and homogenization, and to accelerate dough development, in addition to being used as baking additives as functional ingredients for maintaining dough elasticity, as well as to adjust the gluten quality of flour. In addition, L-cysteine has been used as curing and tenderizing agents in meat products, as well as a stabilizer in milk and dietetic foods. L-cysteine also exhibits antioxidative stabilization in mayonnaise, in addition to antioxidative stabilization and activation in dry yeast. L-cysteine has also been used as a colorant for ham, sausage, bacon and similar meats. In addition, L-cysteine is known to function as an antibrowning agent, and a stabilizer for vitamin C in fruit juice concentrates. Related to this, U.S. Pat. No. 3,352,691, discloses the use of 0.05 to 0.3% cysteine to prevent pink discoloration of comminuted white onions.
Notwithstanding the various alternatives which have been suggested and tried by the prior art over the years to find effective anti-browning agents and preservatives, sulfite continues to be generally recognized as the most effective chemical agent useful for minimizing discoloration of fruits and vegetables, and notably potatoes, processed by commercial production methods.
Nevertheless, there has been a growing concern for and an aversion to the use of sulfites in food products. Recently, the use of sulfites has been banned by the Food and Drug Administration for treating fresh fruits and vegetables. In view of the related concerns expressed for the use of sulfites in processing produce, there is a real need for a preservative composition which minimizes or completely eliminates the need for sulfites in the preservation of produce without compromising the effects on inhibiting or preventing the occurrence of browning reactions.
The present invention, therefore, is directed to compositions and methods for treating produce, and particularly processed potatoes, such as dehydrated potatoes, i.e., potato granules, with a composition including cysteine so as to prevent the adverse effects of enzymatic and non-enzymatic browning. In accordance with the present invention, the processing of produce involves subjecting produce to a composition containing synergistically effective amounts of cysteine, in combination with calcium chloride and sodium acid pyrophosphates, and/or relatively minor amounts of a sulfiting agent, in a manner which results with a finished product containing less than about 50 ppm, and preferably less than 30 ppm sulfite, but most preferably wherein the finished product contains less than 10 ppm or essentially no sulfite.